1. Field of the Invention
The present invention relates to a power distributing device for a vehicle and more particularly to an apparatus for selectively distributing power to the rear wheels or to the front and rear wheels for four-wheel-drive according to the condition of the road.
2. Description of the Prior Art
In known apparatus of the type with which the present invention is concerned, a power distributing device is provided for selectively operating the power train corresponding to various driving conditions, for instance, to a rear-wheel-drive condition in which power is not transmitted to the front wheels but transmitted to rear wheels only in low load and high speed driving, to a power distributing four-wheel-drive condition in which power is distributed properly to both front and rear wheels in heavy duty driving requiring large driving power, and to a direct four-wheel-drive condition in which power is directly transmitted to front and rear wheels without distribution in driving on sand or in mud.
In an apparatus of this type disclosed in a Japanese Official Gazette for Unexamined Utility Model Application No. 151543/1977 (Laid open date Nov. 17, 1977), a ring gear of a plane planetary gear train is connected with an output shaft for transmitting power to the rear wheels, a planet carrier carrying planet gears of the gear set is engaged with a gear driven by an output shaft of a transmission of the vehicle and the sun gear of the gear set is selectively engaged with a stationary portion of the apparatus, with an output shaft transmitting power to the front wheels or with the planet carrier. This device facilitated the operation by arranging the operating positions of an operating lever for the rear-wheel-drive condition and the power distributing four-wheel-drive condition, which are frequently selected adjacent to each other, and by arranging the position for the direct four-wheel-drive condition, which is less frequently selected, on the reverse side of the position for the power distributing four-wheel-drive condition but on the other side with respect to the rear-wheel-drive condition. However, feasibility of operation of the device to select the rear-wheel-drive condition and the power distributing four-wheel-drive condition while driving a vehicle is not satisfactory.
A power transmission having a plane planetary gear set disclosed in U.S. Pat. No. 3,426,623, patented Feb. 11, 1969, provides a synchronizing device for selectively operating the change-speed gearing either in direct drive condition or in planetary overdrive condition.
In the transmission, the ring gear of the plane planetary gear set is connected with an output shaft, the planet carrier of the gear set is connected with an input shaft and the sun gear of the gear set is selectively engaged either with a stationary portion of the transmission or with the planet carrier. The synchronizing device for the transmission (i.e. inertia fastening type Borg-Warner synchronizer) is provided for synchronously engaging a sliding tube, slidable only in the longitudinal direction on a member formed integrally on the sun gear, either with the nonrotary member or with peripheral teeth on the planet carrier.
However, more additional provision of a power distributing device for a four-wheel-device vehicle of the combined power train of a plane planetary gear set and a synchronizing device disclosed in U.S. Pat. No. 3,426,623, is disadvantageous in view of the capacity of the synchronizing device, and furthermore, there is difficulty in applying the aforementioned combined power train to a power distributing device having more than three operational positions including direct four-wheel-drive condition.